Technical Field
The present invention relates generally to adhesive used in the manufacture of corrugated paperboard. More particularly, the present invention relates to the method of manufacturing the adhesive used in the fabrication of corrugated paperboard. Specifically, the present invention provides a method of mixing a set of mixtures and solutions in a series of distinct and non-continuous time segments to create an adhesive composition for use in attaching at least one liner material to a corrugated medium material.
Background Information
Corrugated paperboard is produced when a sheet of medium material, usually a strong paper made largely of bleached or unbleached sulfate pulp, is corrugated by passing through a corrugating machine. Upon leaving the corrugating machine, the corrugated medium material has a series of flutes formed in a sinusoidal shape when viewed from the side. Adhesive is applied to the crests or apexes of the flutes by a glue applicator roll. Then, a first liner is attached to the corrugated medium atop the adhesive. Thereafter, a second adhesive applicator applies additional adhesive to the flutes spaced opposite the first set of flutes. Then, a second liner is connected to the second set of flutes to create a double-faced sheet of paperboard.
In most corrugating operations, the corrugating rolls used to corrugate and shape the medium material are at a temperature of approximately 300° F. This heat transfers to the medium material as it extends through the corrugating machine which helps cure the adhesive. The adhesive most often used in paperboard manufacture is often a starch-based adhesive that requires heat and pressure as part of the chemical reaction to gelatinize the starch into a film. Then water must be removed from the adhesive, often by the application of more heat, in order to fully cure the adhesive.
One problem that occurs is that most methods of available to heat paper to its desired temperature for bonding on the corrugator simultaneously remove water as the paper is being heated. One way to combat the resulting water removal is to use an infusion or pre-wetting system such as one that tries to inject steam under the web through the surface of the heating device to reduce this moisture loss. This device is very speed dependent and difficult to control. Additionally, since the typical corrugator continually changes speeds in a matter of seconds, and the current methods of heating paper sometimes respond in minutes, it becomes difficult to achieve specific temperature and moisture content independently of one another.
The flatness or dimensional stability of a finished paperboard product is often dependent on the moisture balance between the two outside liners that are bonded to the inner corrugated medium paper web. After the three pieces are combined into a sheet of paperboard, the individual sheets of paper often lose or gain moisture to or from one another and the surrounding atmosphere until an equilibrium condition is reached. In order to achieve optimum flatness, the individual sheets of paper should gain or lose as little moisture as possible during the process and should be as close to their equilibrium moisture as possible upon exiting the corrugating machine. This way, post-warp may be minimized.
Many manufacturers of paperboard have improvised types of improvements and have gained patents on new and unique ways to prevent paperboard warping during manufacture. Namely, U.S. Pat. No. 8,398,802 issued to Kohler discloses a method of adjusting the moisture content in a traveling web of medium material so that the web of medium material comprises a 6-9% weight percentage by moisture prior to corrugating. Then that web of medium material is heated to nearly 100° C. Then the material is corrugated such that the web of medium material retains the 6-9% weight percentage moisture through the corrugating steps. Kohler discloses that this method reduces warping and prevents an evenly applied cured adhesive.
Further, additional suppliers have sought patent protection on improved adhesive formulas. Name, PCT Application WO 2011/160049 assigned to Cargill Incorporated discloses an improved adhesive composition that contains a reduced amount of solids. The adhesive composition of the '049 Application includes the following components: a starch, a borate, an alkaline hydroxide, and a rheology modifier. To make the adhesive composition, the '049 Application requires that the components are all added together at one time into an amount of heated water in the range of 50° C.-59° C. (122° F.-138.2° F.), the solution is quenched with water, then reheated to a temperature in the range of 32° C.-44° C. (89.6° F.-111.2° F.), then the solution is mixed continuously for eight minutes to create an adhesive composition. The '049 Application further discloses using nearly 50% less adhesive than ordinarily used in a paperboard manufacturing process. However, in order to do so, the '049 Application requires that the liner temperatures are controlled and constrained in a range of 70-90° C.
From an academic standpoint, the '049 Application reduces the amount of solids within the adhesive in the paperboard manufacturing process. However, it is has been realized that real world applications do not often yield expected results and raise additional issues propagating manufacturing concerns that must be addressed. The present invention addresses these and other issues to cure the concerns.